(1) Field of the Invention
The present invention relates to a solid-state imaging device and a method for manufacturing the solid-state imaging device for sensitivity improvement and flare reduction.
(2) Description of the Related Art
In recent years, coupled with miniaturization of chip size and increase in the number of pixels in a solid-state imaging device, miniaturization and sophistication of a movie camera and the like have been advanced.
A conventional solid-state imaging device disclosed in Japanese Unexamined Patent Application Laid-Open Publication No. 4-34977 (Patent Reference 1) will be described with reference to the drawings.
As shown in FIG. 1, an effective pixel region 102, an optical black (OB) region 103, and a peripheral region 104 are formed on a semiconductor substrate 100 by diffusion processes. After a planarizing film is applied, a resist containing a black pigment for improving a flare property (an antireflection film 110) is formed above the peripheral region 104 excluding at least the effective pixel region 102 and the OB region 103. Further, a transparent film (intermediate film) 108 under microlens is formed which is designed to have a desirable film thickness for planarizing a step created by the formation of the antireflection film 110 and maximizing a light collection effect. Microlenses 109 are formed thereon.
In other words, the antireflection film 110 having black color and the like is arranged to reduce flare occurring when high-luminance light enters the peripheral region 104. Transmittance of the antireflection film 110 is preferably equal to or less than 20% for flare reduction, and thus above a certain thickness is required for this reason. In addition, the microlenses 109 are formed to improve sensitivity of the solid-state imaging device.
However, as miniaturization of cell in a solid-state imaging device is advanced by downsizing a camera, in the conventional solid-state imaging device shown in FIG. 1, it is difficult to shorten a distance from light receiving units to microlenses, and light collection optimization is limited (the first problem).
The reason for such a problem will be described using FIG. 2.
FIG. 2(a) shows a cross-sectional structure of an effective pixel region of a large cell, and FIG. 2(b) shows a cross-sectional structure of an effective pixel region in the case where an intermediate film under miniaturized microlens cannot be thinned. As shown in FIG. 2(a), one of the microlenses 109 allows light to focus on one of light receiving units 101 in the pixel region having a large cell with relative ease. In contrast, as shown in FIG. 2(b), when being miniaturized, the microlens 109 does not allow light to focus on the light receiving unit 101 (a focus is above the light receiving unit 101), which makes the light collection optimization difficult. In particular, as a light collection property for oblique light component is worsened, sensitivity deterioration at a side where aperture is opened becomes remarkable as a camera (the second problem).
Moreover, although it is necessary to increase pigment concentration to perform film thinning on a resist containing a black pigment while maintaining transmittance characteristics, the current technique does not allow significant film thinning easily, and it is not easy to perform the film thinning while maintaining a flare prevention effect (the third problem).
Furthermore, although, as another proposal, it is conceivable that, in order to shorten a distance from the light receiving unit 101 to the microlens 109, at least the antireflection film 110 is arranged in the peripheral region 104 excluding the effective pixel region 102 and the OB region 103 after the microlens 109 is formed in advance, a problem arises that the antireflection film 110 cannot be formed on a surface of the solid-state imaging device as the antireflection film 110 has weak solvent resistance (the fourth problem).
An object of the present invention is to provide a solid-state imaging device that realizes the sensitivity improvement while maintaining the flare prevention effect even when the miniaturization of cell is advanced.